An active-matrix drive liquid crystal display device using thin-film transistor (TFTs) has a structure in which liquid crystal is sandwiched between two opposing substrates, namely a TFT array substrate in which a plurality of TFTs and a plurality of pixel electrodes are formed in a matrix array, and a color filter substrate covered by counter electrodes. For example, a conventional liquid crystal display device described in Patent Document 1 is a vertically aligned liquid crystal display device that includes a glass substrate 110; a TFT substrate 102 having a TFT 105 formed on the TFT substrate 102 and a pixel electrode 124 connected to the TFT 105; a counter substrate 102a arranged to be opposed to the TFT substrate 102; and a vertically aligned liquid crystal 126 sealed between the TFT substrate 102 and counter substrate 102a (see FIG. 24).
Further, in the liquid crystal display device described in Patent Document 1, depressions 123 where portions of the pixel electrode 124 are recessed are provided within the pixel region in which the pixel electrode 124 of TFT substrate 102 has been formed, and etching-stop patterns 113a, 113b, 113c are formed below the depressions 123. When a voltage is applied across the pixel electrode 124 and a common electrode 136, the liquid crystal molecules in the vertically aligned liquid crystal 126 become aligned in a direction perpendicular to the electric field. By forming the depressions 123, therefore, the directions of alignment of the liquid crystal molecules become different from one another radially outward from the depressions 123 and multi-domains are achieved. Further, by forming the etching-stop patterns 113a, 113b, 113c, etching is not allowed to progress owing to the etching-stop patterns 113a, 113b, 113c when the depressions 123 are formed by etching and a decline in the strength of the glass substrate 110 is prevented.    [Patent Document 1] Japanese Patent Kokai Publication No. 2006-243494A
However, with the liquid crystal display device described in Patent Document 1, the etching-stop patterns 113a, 113b, 113c are made of metal (e.g., laminated films of aluminum and titanium) and light cannot pass through them. The result is a small aperture ratio. (If a pixel is divided into a portion that transmits light and a portion that does not, the aperture ratio is the area ratio of the portion that transmits light). Thus, there is much to be desired in the art.
It is an object of the present invention to provide a vertically aligned thin-film transistor array substrate that does not result in a reduced aperture ratio, a method of manufacturing the substrate and a liquid crystal display device having the substrate.
According to a first aspect of the present invention, there is provided a thin-film transistor array substrate comprising: an etching-stop layer formed on an insulating layer; a passivation layer formed on the insulating layer that includes the etching-stop layer; a depression formed in the passivation layer and hollowing the passivation layer to the surface of the etching-stop layer; and a pixel electrode, which is recessed in conformity with the depression, formed on the passivation layer including the depression; wherein the etching-stop layer comprises a transparent semiconductor.
According to a second aspect of the present invention, there is provided a thin-film transistor array substrate comprising: a pixel protrusion formed on an insulating layer; a passivation layer formed on the insulating layer that including the pixel protrusion and having a first projecting portion corresponding to the pixel protrusion; and a pixel electrode formed on the passivation layer including the first projecting portion and having a second projecting portion corresponding to the first projecting portion; wherein the pixel protrusion comprises a transparent semiconductor.
According to a third aspect of the present invention, there is provided a liquid crystal display device comprising the above-described thin-film transistor array substrate; a color filter substrate; and a liquid crystal layer interposed between the thin-film transistor substrate array and the color filter substrate.
According to a fourth aspect of the present invention, there is provided a method of manufacturing a thin-film transistor array substrate comprising: forming a gate electrode and a scanning line on a transparent insulating substrate; forming an insulating layer on the transparent insulating substrate that includes the gate electrode and the scanning line; and forming a transparent semiconductor layer on the insulating layer in an area which will become a channel of the gate electrode, and simultaneously forming on the insulating layer an etching-stop layer consisting of a material identical with that of the transparent semiconductor layer. The method further comprises: forming at least a drain electrode, a source electrode and a signal line on the insulating layer; forming a passivation layer on the insulating layer that includes the transparent semiconductor layer, the etching-stop layer, the signal line, the drain electrode and the source electrode; and forming a depression, which hollows the passivation layer to the surface of the etching-stop layer, in the passivation layer, and simultaneously forming a contact hole that communicates with the source electrode. The method further comprises: forming a pixel electrode on the passivation layer that includes areas of the depression and the contact hole.
According to a fifth aspect of the present invention, there is provided a method of manufacturing a thin-film transistor array substrate comprising: forming a gate electrode and a scanning line on a transparent insulating substrate; forming an insulating layer on the transparent insulating substrate that includes the gate electrode and the scanning line; and forming a transparent semiconductor layer on the insulating layer in an area which will become a channel of the gate electrode, and simultaneously forming on the insulating layer a pixel protrusion consisting of a material identical with that of the transparent semiconductor layer. The method further comprises: forming at least a drain electrode, a source electrode and a signal line on the insulating layer; forming a passivation layer on the insulating layer that includes the transparent semiconductor layer, the pixel protrusion, the signal line, the drain electrode and the source electrode; and forming a contact hole, which communicates with the source electrode, in the passivation layer. The method further comprises: forming a pixel electrode on the passivation layer that includes areas of the pixel protrusion and the contact hole.
In accordance with the present invention (first and third aspects), the etching-stop layer in the pixel region is transparent. As a result, the aperture ratio (the area ratio of the portion that transmits light in a case where a pixel is divided into a portion that transmits light and a portion that does not) can be enlarged and a liquid crystal display device exhibiting an excellent display characteristic is obtained.
In accordance with the present invention (second and third aspects), the pixel protrusion in the pixel region is transparent. As a result, the aperture ratio (the portion that transmits light in a case where a pixel is divided into a portion that transmits light and a portion that does not) can be enlarged and a liquid crystal display device exhibiting an excellent display characteristic is obtained.
In accordance with the present invention (fourth aspect), the etching-stop layer can be formed at the same time as the transparent semiconductor layer of the thin-film transistor. As a result, there is no increase in photoresist-forming steps and no increase in device manufacturing cost.
In accordance with the present invention (fifth aspect), the pixel protrusion can be formed at the same time as the transparent semiconductor layer of the thin-film transistor. As a result, there is no increase in photoresist-forming steps and no increase in device manufacturing cost.